A mud volcano that is erupting in Indonesia was most probably caused by drilling for gas, according to the first published scientific study. The event forced the evacuation of many villages, and will leave 11,000 people permanently displaced.
The study concludes that the eruption appears to have been triggered by drilling of over-pressured porous and permeable limestones. The study is published in the magazine of the Geological Society of America, GSA Today.
The volcano is disgorging between 7000 and 150,000 cubic metres (245,000 and 5.25 million cubic feet, respectively) of mud every day and the flow “will continue for many months and possibly years to come”, the report warns.
In the coming months, subsidence will occur over an area several kilometres wide and there is likely to be “more dramatic collapse” around the main vent, forming a crater.
An area of at least 10 square kilometres (3.9 square miles) around the volcano will be uninhabitable for years, say the researchers, led by Richard Davies, at the University of Durham, UK. The British experts analysed satellite images of the area to make their study.
The volcano, known locally as Lusi, has been spewing steaming mud since 29 May 2006, submerging four villages, fields and factories. It erupted from a gas well near Surabaya, East Java, that was operated by Lapindo Brantas Inc.
The scientists say that seepage of mud and water are usually a preventable hazard when exploring for oil and gas. “It is standard industry procedure that this kind of drilling requires the use of steel casing to support the borehole, and protect against the pressure of fluids such as water, oil or gas,” says Davies.
“In the case of Lusi, a limestone water aquifer was drilled into while the lower part of the borehole was not protected by casing,” he says. The aquifers are about 3 km (1.9 miles) below the surface.
The report adds: “The borehole provided a pressure connection between the aquifers in the limestones and overpressured mud in overlying units. As this was not protected by steel casing, the pressure induced hydraulic fracturing, and fractures propagated to the surface, where pore fluid and some entrained sediment started to erupt.”
No quake link
Davies said the case in Indonesia was similar to a blowout that happened off the shore of Brunei in 1979: “Just as is most probably the case with Lusi, the Brunei event was caused by drilling and it took an international oil company almost 30 years and 20 relief wells before the eruption stopped.”
Last week, Indonesia’s minister for social welfare, Aburizal Bakrie, whose family firm controls Lapindo Brantas, said the volcano was a “natural disaster” unrelated to the drilling activities.
“It is not because of the Lapindo drill but it is because of the quake,” he said, referring to an earthquake on 27 May 2006 near the ancient city of Yogyakarta that killed around 6000 people.
But this scenario is ruled out by the study. It concludes that the quake was not to blame, mainly because two days elapsed before mud volcano erupted, and no other mud volcanoes occurred in the region after the quake.
In December 2006, President Susilo Bambang Yudhoyono ordered Lapindo to pay 3.8 trillion rupiah ($421 million) in compensation and costs related to the mud flow.